This invention relates to a method and apparatus for monitoring and displaying the condition of muscles in a muscle group by the sensing and analysis of electromyographic signals derived from a non-invasive body surface electrode array positioned close to the muscle group. Particularly this invention relates to an electrode apparatus and a system for positioning and holding electrodes in a desired orientation relative to the anatomy of a patient.
Knowledge of the presence of electromyographic (EMG) signals in the muscles of humans, and the change of these signals with muscle activity, spawned development of electronic devices and techniques for monitoring those signals for the evaluation of the muscles. Human musculature, however, involves many hundreds of muscles in various muscle groups, which interact to provide skeletal support and movement. Much of the recent development has been concerned with the techniques and/or devices for monitoring the signals, analyzing the information obtained and providing reliable and useful data for the patient or treating physician. Recent developments in computer technology have also provided an assist in this regard. With higher speeds of operation and greater computing capacity, the capability for handling and operating upon a multiplicity of signals in a reasonable evaluation period has become feasible. However, because of the complexity of the muscle structure and the difficulty in obtaining useful, reliable signals, preferably in a non-invasive mode, obtaining a useful definition of the muscle activity in a reasonable amount of time and in an economical manner is still subject to current development.
Typical of this prior art is the device described by D. Prutchi in the publication xe2x80x9cA High-Resolution Large Array (HRLA) EMG Systemxe2x80x9d, published September 1995 in Med. Eng. Phys., Vol. 17, 442-454. Prutchi describes a bracelet which may be wrapped about a body limb and which contains 256 surface electrodes to record the electrical activity of underlying muscles. The electrodes are arranged in eight groups of thirty-two electrode linear arrays directly connected to buffer boards in close proximity of the electrodes. Further processing of the electrical signals is performed to provide a desired signal analysis, in this instance primarily being concerned with the bidirectional propagation of a compound potential in a single muscle in the upper arm of a human subject or a histogram of total power contribution from active fibers in a subject muscle, both being presented in charted format.
U.S. Pat. No. 5,086,779 to DeLuca, et al., describes a back analysis system of plural electrodes coupled to a computer system for processing the signals and to provide graphical representations of results. DeLuca""s invention relates primarily to isolating particular muscle groups by the use of support and restraint devices which limit the movement of the patient""s torso in predetermined patterns correlated to the desired muscle groups. DeLuca""s electrode array consists of separate electrodes individually placed at desired locations on a patient""s back.
U.S. Pat. No. 5,058,602 to Brody describes a method of electromyographic scanning of paravertebral muscles comprising measuring electrical potentials bilaterally across segments of the spine. Readings are categorized into different patterns which are indicative of different muscular conditions. Brody suggests equipment useful within his described techniques as an available EMG scanner having electrodes spaced 2.5 cm apart and a computer component, but provides few details on the equipment or an indication of usefulness for isolating certain muscles or muscle groups.
U.S. Pat. No. 5,318,039 to Kadefors, et al., describes a method and apparatus for detecting electromyographic signals, processing them and providing an indication of the change of the signal from a predetermined norm. Kadefors"" electrode system comprises three electrodes, one of which is a reference marker. This electronic apparatus, in essence, includes a sample and hold function in which current responses can be compared to earlier responses and an indication provided based on the differences detected.
U.S. Pat. No. 5,505,208 to Toormin, et al., describes a method for determining the status of back muscles wherein EMG signals are monitored from a number of electrodes placed in a pattern on a patient""s back, the activity of each electrode is determined and the results stored. A database of results provides a standard from which comparisons can be made to determine deviations or abnormalities, as a device for the care and management of the patient""s dysfunction.
U.S. Pat. No. 5,513,651 to Cusimano, et al., describes a portable electronic instrument for monitoring muscle activity, using standard ECG electrodes and a computer for analyzing the detected signals. The electrodes are applied individually at predetermined locations and a range of motion device is employed to generate signals related to a particular muscle group. Output plots are produced to provide an indication of results, apparently in the form of printouts of information reflecting any deviations from the norm of expected muscle activity.
While the prior art devices describe much sophistication in the detection and analysis of EMG signals, there is a need for equipment which is capable of being utilized by the average skilled examining physician who, for example, uses and is familiar with the techniques of physical examination and palpation of the paraspinous musculature of the thoracolumbosacral spine.
An object of the present invention is to provide improved surface EMG equipment, readily useable by the skilled examining physician, for the diagnosis or treatment monitoring of patients with low back pain.
A further object of the present invention is to provide an improved clinical tool which is portable and which uses non-invasive techniques for the collection of signals.
A further object of the present invention is to provide improved EMG equipment which provides a visual display of the activity of muscles or muscle groups.
A further object of the present invention is to provide improved EMG equipment in which the visual display of muscle activity is juxtaposed over a visual display of normal muscle anatomy for correlation by the examining physician.
A further object of the present invention is to provide improved EMG equipment in which the visual display can be selected for specific musculature identified by the examining physician.
A further object of the present invention is to provide improved EMG equipment which utilizes a single detector pad of electrodes in which the electrodes are arranged in a specific array, to monitor instantaneously all specific muscles in a muscle group of a patient.
A further object of the present invention is to provide an improved electrode.
A further object of the present invention is to provide an improved EMG electrode which achieves better signal acquisition.
A further object of the present invention is to provide an improved electrode that is easier to manufacture.
A further object of the present invention is to provide an electrode with an ornamental design.
A further object of the present invention is to provide an improved electrode array.
A further object of the present invention is to provide an improved system for holding an electrode array in contact with a patient.
A further object of the present invention is to provide an improved method for positioning an electrode array relative to the anatomy of a patient.
A further object of the present invention is to provide an improved EMG diagnostic system which provides enhanced correspondence between collected data and the anatomy of the particular patient.
A further object of the present invention is to provide an inexpensive flexible electrode array.
A further object of the present invention is to provide an electrical connector between an electrode array and a buffer/amplifier that minimizes wear between contact points.
Further objects of the present invention will be made apparent in the following Best Modes for Carrying Out the Invention and the appended Claims.
The electromyographic (EMG) diagnostic system of the present invention is particularly suited for evaluation of the lower back of a human and consists essentially of a sensor pad for collecting and conditioning EMG signals, electronic equipment including a computer for signal discrimination and evaluation and a display device for providing a visual display of the activity of selected musculature. A ground electrode is positioned on the patient. The electronic equipment serves to receive signals from the sensor pad which is pressed against the lower back of a patient in a predetermined location and held immobile relative to the patient such as by strap with foam backing, an inflatable bladder, an adhesive pad, disposable or reusable patient adhering structures or other convenient arrangement. Signals from individual electrodes are conditioned by the electrical equipment, discriminated from noise signals and the like and evaluated relative to the signal received from the reference electrode. Computer apparatus is then used to analyze the signals, and can combine the signals in various patterns to provide an analysis of the muscular anatomy of the lower back and the activity of such muscles.
In an exemplary form of the invention electrodes are used which have a plurality of projections in either a pyramid or conical shape. The configuration enhances acquisition of signals from the underlying muscles and reduces extraneous signals produced by electrolytic and other reactions with the skin of the patient and adjacent support structures. Such electrodes are preferably arranged in an array supported on a web or pad structure. The web or pad structure is preferably flexible to conform to the contours of the patient""s anatomy. The pad structure is preferably part of or connected to a releasable adhesive that adheres to the patient""s skin without relative movement until removed. The supporting web or pad structure for the electrodes may be reusable or disposed of after a single use.
Alternatively, an inexpensive flexible array of electrodes is formed by depositing or printing conductive inks in the shapes of circular electrodes on a flexible and extensible substrate sheet. A flexible conductive adhesive such a hydrogel is deposited on the printed electrodes to increase the sensitivity of the electrodes and to adhere the electrodes to the skin surfaces of a patient. Trace lines are also printed on the substrate to route electrical signals from each electrode to a portion of the substrate that is operative to connect with signal processing components such as a buffer/amplifier.
One exemplary technique for signal monitoring is to determine the RMS voltage of the sensed signals over a predetermined time interval. The RMS voltage is converted to a visual display representative of the power level, which display then provides a visual indication of those locations where a higher level of muscle activity is detected. The RMS signal technique is advantageous in providing a device for averaging the highly sensitive and often variable individual electrode signals which are susceptible to changes in contact resistance at the electrode, the human skin resistance, stray field fluctuation, inadvertent movements by the patient, and the like, which can introduce false signals, and mask the desired muscle activity signals.
A visual display of the sensed muscle activity is provided on a monitor, such as a cathode ray tube type monitor, which may then be evaluated by the attending physician. A predetermined display of normal back anatomy is displayed simultaneously as an underlay on the monitor to assist the physician in his evaluation. For example colorization of the resultant sensed display with different colors representing the degree of contraction thus provides a vivid indication of abnormal activity of the muscle. The display is modified to correspond to the anatomy of the patient. Normal back anatomy is provided in this invention by the selection from an inventory of various back muscle configurations which depict different layers of back muscles of the normal human patient. These configurations are selectable by the physician for comparison with the sensed muscle activity pattern in order to assist in providing a correlation between the two. Further control is provided in that the physician not only can alter the physical configuration of the sensed signal display but also can adjust the intensity or colorization of the sensed display to render a more pronounced image of abnormal muscle activity relative to normal back anatomy. Visual display modification is achieved by adjustment of the sensitivity of the sensed signal detector or by increasing the level of signal over which a visual indication is provided.